Does thicker ice cover cause stronger glacially triggered earthquakes? - A case study from the southwestern Baltic Sea

Increasing and decreasing ice masses cause an isostatic adjustment of the crust, which can trigger fault reactivation. It could be assumed that the higher the ice load, the stronger the glacially induced fault reactivation, leading to stronger earthquakes. Here we focus on glacially triggered fault reactivation in the southern Baltic Sea over the past 200,000 years (since the Upper Saalian). Our study area comprises the Caledonian Suture Zone between the East European Craton and the West European Platform as well as the trans-regional Tornquist Zone. Consequently, it reflects a polyphase tectonic history. The fault zones and systems in this geoarchive have been mapped and studied through several reflection seismic investigations. They display variations in their characters, strike and dip directions, age, and depths, documenting the complex evolution.

We focus on faults indicating reactivation during the Quaternary, determined by the seismic sections. After documenting their fault properties, we calculated the glacially induced Coulomb Failure Stress changes (∆CFS) at the faults over the past 200,000 years using finite-element simulations of various glacial isostatic adjustment models. The results show significant local and temporal differences in fault reactivation. We observe that shorter ice advances and lower ice loads correlate with higher ∆CFS, suggesting a higher potential for fault reactivation, which could potentially lead to stronger earthquakes if released in one event. Moreover, we will discuss if the lateral ice thickness gradient or the steepness of the flanks of the ice sheet might play a major role.